Mechanisms of reaction of aminoxyl (nitroxide), iminoxyl, and imidoxyl radicals with alkenes and evidence that in the presence of lead tetraacetate, N-hydroxyphthalimide reacts with alkenes by both radical and nonradical mechanisms

[GRAPHICS] 1,2-Dideuterio-cyclohexene, 1,2-dideuterio-cyclooctene, and trans-3,4-dideuterio-hex-3-ene were reacted with three > NO. radicals: 4-hydroxyTempo, di-tert-butyliminoxyl, both used as the actual radicals, and phthalimide-N-oxyl (PINO) generated from N-hydroxyphthalimide (NHPI) by its reaction with tert-alkoxyl radicals (t-RO.) and with lead tetraacetate. In all cases, except the NHPI/Pb(OAc)(4) system, only mono > NO-substituted alkenes were produced. The H-2 NMR spectra imply that 88-92% of monoadducts were formed by the initial abstraction of an allylic H-atom, followed by capture of the allylic radical by a second > NO., while the remaining 12-8% appear to be formed by an initial addition of > NO. to the double bond followed by H-atom abstraction by a second > NO.. A substantial and sometimes the major product formed with the NHPI/Pb(OAc)(4) system has two PINO moieties added across the double bond. Since such diadducts are not formed with the NHPI/t-RO. system, a heterolytic mechanism is proposed, analogous to that known for the Pb(OAc)(4)-induced acetoxylation of alkenes. A detailed analysis of the NHPI/Pb(OAc)(4)/alkene products indicates that monosubstitution occurs by both homolytic and heterolytic processes.